On the synopses my professor has been passing out, he includes passive prohibitions in the singular and plural. I imagine that one would make nollo into a passive imperative the same way that deponent imperatives are formed (nolle - sg, nolimini - pl) then supply the passive infinitive of whatever verb. So for say sedeo: nolle sederi - sg, nolimini sederi - pl.

For a passive prohibition, you have several choices (though your idea of making nolle passive is not one of them as there are no passive forms for this verb, I'm sorry to report). Did your professor give you an idea of which construction he/she wanted you to use?

One classical choice is ne + perfect subjunctive [either active or passive as the sense requires]. So, "Do not be silent" [spoken to a male] would be "Ne sis tacitus!" or [spoken to a female] "Ne sis tacita!"